[Intel-gfx] [PATCH] drm/i915: vlv: fix IRQ masking when uninstalling interrupts

[Daniel Vetter]

On Thu, Nov 20, 2014 at 04:05:55PM +0200, Imre Deak wrote:
> irq_mask should include all IRQ bits that we want to mask, but atm we
> set it incorrectly to the inverse of this. If the mask is used
> subsequently to enable/disable some IRQ bits, we may unintentionally
> unmask unrelated IRQs. I can't see any way that this can lead to a real
> problem in the current -nightly code, since the first place the mask
> will be used next (after a suspend/resume cycle) is in
> valleyview_irq_postinstall(), but the mask is reset there to its proper
> value.
> 
> This causes a problem in the upstream kernel though, where - due to another
> issue - the mask is used in the above way to disable only the display IRQs.
> This other issue is fixed by:
> 
> commit 950eabaf5a87257040e0c207be09487954113f54
> Author: Imre Deak <imre.deak at intel.com>
> Date:   Mon Sep 8 15:21:09 2014 +0300
> 
>     drm/i915: vlv: fix display IRQ enable/disable
> 
> Interestingly, even with the above two bugs, we shouldn't in theory have
> any real problems (arguably a famous last sentence:). That's because
> even if we unmask something unintentionally via the VLV_IMR/VLV_IER
> register the master IRQ masking bit in VLV_MASTER_IER is still set and
> should prevent all i915 interrupts. According to my testing on an ASUS
> T100 with DSI output this isn't the case at least with the
> MIPIA_INTERRUPT. Leaving this one unmasked in IMR/IER, while having
> VLV_MASTER_IER set to 0 may lead to a lockup during system suspend as
> shown in the bugzilla ticket below. This fix should get rid of the
> problem reported there in upstream and older kernels.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=85920
> Cc: stable at vger.kernel.org (v3.15+)
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_irq.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 8d169e1..4601f53 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -3597,7 +3597,7 @@ static void vlv_display_irq_uninstall(struct drm_i915_private *dev_priv)
>  
>  	vlv_display_irq_reset(dev_priv);
>  
> -	dev_priv->irq_mask = 0;
> +	dev_priv->irq_mask = ~0;

vlv seems to be the only platform which resets irq masks in the uninstall
hook. That smells fishy - can't we just remove this completely?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch